Lining processes in which curable synthetic resin is used are known, and typical of such a process is described in British patent specification no. 1449455. As described in that patent specification, a lining process for an underground passageway such as a sewer involves the use of a flexible lining tube which comprises a resin absorbent inner layer such as a fibrous felt, and an impermeable outer layer. To insert the flexible tube into the pipeline or passageway to which the tube is sized, the tube is everted using fluid pressure, typically a head of .water. The resin impregnated fibrous inner layer is therefore turned inside out and is presented to the surface to be lined. When the lining tube has been applied fully, the resin soaking the absorbent layer is cured so that in fact the resin absorbent layer and the cured resin form a rigid lining shell or skin on the passageway surface. The impermeable membrane may serve as a surface to the finished tube, or it may alternatively be removed. This lining process is extremely successful and is used throughout the world and is in fact known as the Insituform (Registered trademark) process. The flexible lining tube comprising the inner fibrous layer and the outer impermeable layer is trademarked by the name Insitutube.